Scaling is a precipitation that occurs in hot tubs, like barnacles on the hull of a boat. It happens when the spa water maintains a constant high calcium hardness, pH, or total alkalinity level. Scaling can occur on both internal spa components and the surface of the spa shell. The longer it remains on the spa surface the more difficult it is to remove. Since it is only the result of poor water maintenance or hard source water it is not covered by any spa manufacturer’s warranty. Using HT Stain & Scale is your best prevention from scaling.